Some current laser ablation masks are fabricated by using apertured alternating layers of dielectric materials. For example, U.S. Pat. No. 4,923,772, issued to Steven J. Kirch et al. on May 8, 1990 and assigned to the present assignee, discloses an ablation mask having multiple dielectric layers of alternating high and low indices of refraction on a U.V. grade synthetic fused silica substrate. The described mask withstands the fluences of the high energy and high power lasers employed therewith. However, these masks are relatively expensive and complicated to fabricate and the constituent dielectric material is tailored for use with a particular wavelength laser. Hence, when the laser ablation wavelength changes, for example, when different target materials are desired to be ablated, a new dielectric mask with different dielectric material is required. U.S. Pat. No. 5,349,155 teaches the use of a similar mask.
Another type of laser ablation mask known in the art uses an apertured single layer or an apertured composite metal layer on a quartz substrate. Chromium, aluminum and copper-backed aluminum have been suggested for use as the metal. Brief mention is made in the aforementioned U.S. Pat. No. 4,923,772 that aluminum can be used as the metal provided that the energy density or fluence of the laser is in the range below 200 mJ/cm.sup.2. The patent notes that patterned aluminum-on-silica masks cannot withstand the full range of the very high laser fluences encountered and that dielectric coated silica masks are preferred in the ranges of fluence greater than 100 mJ/cm.sup.2. Chromium suffers the same damage disadvantage as does aluminum at about 200 mJ/cm.sup.2 laser energy densities according to the teachings of aforementioned U.S. Pat. No. 4,923,772. It is to be noted that no mention is made of the thicknesses of the mask metal in the examples cited in the patent. Further citation of the use of chromium on quartz ablation masks is given in U.S. Pat. No. 4,786,358.
IBM Technical Disclosure Bulletin, entitled "Metal Films/Diamond Membrane Mask for Excimer Laser Ablation Projection Etching", Vol. 36, No. 11, pp. 583-584, (November 1993), describes a 3-5 .mu.m thickness of aluminum deposited on CVD diamond and covered by an anti-reflecting coating for use as a laser ablation mask. The purpose of the diamond is to efficiently heat-sink the laser energy absorbed by the aluminum throughout the laser pulse duration. The described mask structure is somewhat expensive and complicated to fabricate. In the case where copper is substituted for diamond in order to provide similar heat dissipation, the formation of alloys of copper and aluminum at the aluminum-copper interface reduces the reflectance of the aluminum and increases the risk of metal mask feature destruction at high laser fluence.